The present invention generally relates to fabrication of semiconductor integrated circuits and more particularly, to an apparatus and method for detecting material accretion and dislodging from a quartz gas distribution plate (GDP) in a plasma process chamber during semiconductor wafer processing.
In the semiconductor production industry, various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include the deposition of layers of different materials including metallization layers, passivation layers and insulation layers on the wafer substrate, as well as photoresist stripping and sidewall passivation polymer layer removal. In modern memory devices, for example, multiple layers of metal conductors are required for providing a multi-layer metal interconnection structure in defining a circuit on the wafer. Chemical vapor deposition (CVD) processes are widely used to form layers of materials on a semiconductor wafer.
CVD processes include thermal deposition processes, in which a gas is reacted with the heated surface of a semiconductor wafer substrate, as well as plasma-enhanced CVD processes, in which a gas is subjected to electromagnetic energy in order to transform the gas into a more reactive plasma. Forming a plasma can lower the temperature required to deposit a layer on the wafer substrate, to increase the rate of layer deposition, or both. However, in plasma process chambers used to carry out these various CVD processes, materials such as polymers are coated onto the chamber walls and other interior chamber components and surfaces during the processes. These polymer coatings frequently generate particles which inadvertently become dislodged from the surfaces and contaminate the wafers.
In semiconductor production, the quality of the integrated circuits on the semiconductor wafer is directly correlated with the purity of the fabricating processes, which in turn depends upon the cleanliness of the manufacturing environment. Furthermore, technological advances in recent years in the increasing miniaturization of semiconductor circuits necessitate correspondingly stringent control of impurities and contaminants in the plasma process chamber. When the circuits on a wafer are submicron in size, the smallest quantity of contaminants can significantly reduce the yield of the wafers. For instance, the presence of particles during deposition or etching of thin films can cause voids, dislocations, or short-circuits which adversely affect performance and reliability of the devices constructed with the circuits.
Particle and film contamination has been significantly reduced in the semiconductor industry by improving the quality of clean rooms, by using automated equipment designed to handle semiconductor substrates, and by improving techniques used to clean the substrate surfaces. However, as deposit of material on the interior surfaces of the processing chamber remains a problem, various techniques for in-situ cleaning of process chambers have been developed in recent years. Cleaning gases such as nitrogen trifluoride, chlorine trifluoride, hexafluoroethane, sulfur hexafluoride and carbon tetrafluoride and mixtures thereof have been used in various cleaning applications. These gases are introduced into a process chamber at a predetermined temperature and pressure for a desirable length of time to clean the surfaces inside a process chamber. However, these cleaning techniques are not always effective in cleaning or dislodging all the film and particle contaminants coated on the chamber walls. The smallest quantity of contaminants remaining in the chamber after such cleaning processes can cause significant problems in subsequent manufacturing cycles.
Therefore, it is an object of the present invention to detect the presence of material accretion on interior components of a plasma process chamber during the processing of semiconductors.
A further object of the present invention is to detect the dislodging of potential contaminant particles from an interior surface of a plasma process chamber during the processing of semiconductors.
Still another object of the present invention is to provide for continuous monitoring of a plasma process chamber during the processing and fabrication of semiconductor integrated circuits in order to prevent or minimize particle contamination of one or multiple semiconductor wafers.
Yet another object of the present invention is to provide a mechanism which utilizes differences in brightness, opacity or reflective index of a surface inside a plasma process chamber to reveal material accretion on and/or particle dislodging from the surface for potential wafer substrate contamination.
A still further object of the present invention is to prevent or reduce contamination of a semiconductor wafer substrate inside a plasma process chamber by utilizing multiple light sensors which detect differences in brightness or reflective index of a gas distribution plate (GDP) inside the chamber to monitor material accretion on and/or dislodging of potential contaminating particles from the plate.
In accordance with these and other objects and advantages, the present invention comprises multiple optical sensors which are provided in the top portion of a plasma process chamber above a gas distribution plate of the chamber and are connected to a central process controller that is capable of terminating operation of the chamber and may be equipped with an alarm. In the event that the optical sensors detect relative disparities or asymmetries in brightness or light reflective index among various portions or regions of the gas distribution plate, which disparities or asymmetries may indicate the formation of a material accretion or coating on the plate or dislodging of contaminant particles from the plate, a signal is sent to the process controller, which may be adapted to terminate the plasma process, alert operating personnel, or both.